Set up ls aliases in my bash startup

ls-aliases.sh

# Prefer using eza for my big five ls aliases. If it's not there, then check
# to see if we're on macOS which has different ls flags than Linux's ls.
# Finally, assume we're using Linux.

# From https://stackoverflow.com/questions/592620/how-to-check-if-a-program-exists-from-a-bash-script
if hash eza 2>/dev/null ; then
    base='eza -F -B -g --smart-group --git --no-quotes'
    alias ls="$base"
    alias ll="$base -l"
    alias la="$base -l -aa" # The -aa is intentional.
    alias lt="$base -l --sort=newest"
    alias ltr="$base -l --sort=oldest"
    unset base
elif [[ $OSTYPE =~ ^darwin ]] ; then
    base='ls -GF'
    # Mac has -G for color.
    alias ls="$base"
    alias ll="$base -l"
    alias la="$base -l -a"
    alias lt="$base -l -t"
    alias ltr="$base -l -t -r"
    unset base
else
    base='ls --color=auto -F'
    alias ls="$base"
    alias ll="$base -l"
    alias la="$base -l -A"
    alias lt="$base -l -t"
    alias ltr="$base -l -t -r"
    unset base
fi